[Core] Emit total lineage bytes metric

[jjyao]

Why are these changes needed?

Ray only store task specs for lineage reconstruction up to max_lineage_bytes config and if the limit is reached, some task specs will be evicted and related objects can no longer be reconstructed. Emitting the metric showing the total memory used for storing task specs so that we can better tune the limit.

Related issue number

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[raulchen]

How does the Grafana chart look like?
Will it break down the linage size by workers?

[jjyao]

Will it break down the linage size by workers?

Yes, worker id is a metric tag

[jjyao]